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131.
132.
K?re?KullerudEmail authorView authors OrcID profile Jana?Kotková Vladimír??rein Milan?Drábek Radek??koda 《Contributions to Mineralogy and Petrology》2018,173(9):71
Sulfoselenides [Ag2(S,Se)] and Se-bearing polybasite have been discovered at the Kongsberg silver district. The selenium-bearing minerals occur in two samples from the northern part of the district, forming either single or polyphase inclusions together with chalcopyrite within native silver. The Ag-sulfoselenides show large chemical variations, covering nearly the complete compositional range between acanthite (Ag2S) and naumannite (Ag2Se). For the data presented here, there is no local maximum at the composition Ag4SSe attributed to the distinct phase called aguilarite, suggesting that this composition can be considered as one of many possible along the monoclinic Ag2S–Ag2S0.4Se0.6 solid solution series rather than a specific mineral phase. We present a model explaining the variations in the Se-content of Ag2(S,Se) as a result of gradual de-sulfidization of the rock under oxidizing conditions. During this process, sulfur from the Ag2S-component of Ag2(S,Se) oxidized and dissolved in the fluid phase as SO42?, resulting in the formation of native silver. The activity ratio \({a_{{{\text{S}}^{2 - }}}}/{a_{{\text{S}}{{\text{e}}^{2 - }}}}\) of the system gradually decreased due to the removal of SO42?, which resulted in the stabilization of a sulfoselenide with higher selenium content. As a result of reaction progress, grains of Ag2(S,Se) became gradually enclosed in newly formed native silver, and therefore isolated from further reactions with the grain-boundary fluid. Grains isolated early during the process show low content of Se reflecting high \({a_{{{\text{S}}^{2 - }}}}/{a_{{\text{S}}{{\text{e}}^{2 - }}}}\) of the equilibrium fluid, while grains showing high Se reflect the composition of late low \({a_{{{\text{S}}^{2 - }}}}/{a_{{\text{S}}{{\text{e}}^{2 - }}}}\) fluids. Analyses of Se-bearing polybasite show that selenium is preferentially partitioned into Ag2(S,Se) compared to polybasite. The model presented here demonstrates how oxidation of sulfoselenides leads to fractionation of sulfur and selenium. 相似文献
133.
The paper presents some results of seismic experiments carried out on the territory of northern Moravia and Silesia, roughly
delimited by the coordinates 16°E–19°E and 49°N–51°N. The experiments were aimed at compiling a velocity model of the uppermost
Earth’s crust using the database of arrival times of Pg and Sg waves recorded at a fairly large number of seismic stations, which enabled us to produce a simple 1D-layered velocity model
of the region. The velocity model was computed using the traditional tomographic iterative process composed of consecutive
solutions of linear equations. Based on the analysis of velocity distribution, it was found that the velocities of Pg and Sg waves increase from about 5.9 and 3.3 km/s at the surface, to about 6.1 and 3.5 km/s at a depth of 11 km, respectively. 相似文献
134.
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136.
Nutrient budgets for European seas: a measure of the effectiveness of nutrient reduction policies 总被引:3,自引:0,他引:3
Artioli Y Friedrich J Gilbert AJ McQuatters-Gollop A Mee LD Vermaat JE Wulff F Humborg C Palmeri L Pollehne F 《Marine pollution bulletin》2008,56(9):1609-1617
Socio-economic development in Europe has exerted increasing pressure on the marine environment. Eutrophication, caused by nutrient enrichment, is evident in regions of all European seas. Its severity varies but has, in places, adversely impacted socio-economic activities. This paper aims to evaluate the effectiveness of recently adopted policies to reduce anthropogenic nutrient inputs to European seas. Nitrogen and phosphorus budgets were constructed for three different periods (prior to severe eutrophication, during severe eutrophication and contemporary) to capture changes in the relative importance of different nutrient sources in four European seas suffering from eutrophication (Baltic Proper, coastal North Sea, Northern Adriatic and North-Western Black Sea Shelf). Policy success is evident for point sources, notably for P in the Baltic and North Seas, but reduction of diffuse sources has been more problematic. 相似文献
137.
Quantitative study of a rapidly weathering overhang developed in an artificially wetted sandstone cliff 下载免费PDF全文
Those factors controlling the weathering and erosion of sandstone on the field scale are still not well understood. In this study, a specific sandstone overhang (and its surroundings) with artificially induced and extremely high erosion rates was subjected to a complex investigation. Contrast between the erosion rate of the wet and dry portions of the same cliff enabled isolation of the factors responsible for rapid sandstone retreat. Erosion rates, moisture, and salt content, as well as suction were monitored in the field. Mineral phases and water chemistry were analyzed. The measurement of tensile strength, laboratory frost weathering tests, and numerical modeling of stress were performed. The acquired data show that an increase of moisture content in pores in the area of the studied overhang decreased tensile strength of the sandstone to 14% of its dry value, and increases the sandstone weathering and erosion rate, by nearly four orders of magnitude, compared to the same sandstone under natural moisture conditions outside of the cliff area. Consequently, frost weathering, in combination with wetting weakening was found to play a major role in weathering/erosion of the sandstone cliff and overhang. Frost weathering rate in both the laboratory and field increases up to 15 times with decreasing gravity‐induced stress. The results also indicate that sandstone landforms in temperate climates may potentially develop very rapidly if the pore space is nearly saturated with water, and will later remain relatively stable when the moisture content decreases. As a general implication, it is suggested that overhangs in Central Europe (and elsewhere) might be the result of rapid frost weathering of nearly saturated sandstone during the Last Glacial. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
138.
Solifluction meets vegetation: the role of biogeomorphic feedbacks for turf‐banked solifluction lobe development 下载免费PDF全文
Jana Eichel Daniel Draebing Lasse Klingbeil Markus Wieland Christian Eling Sebastian Schmidtlein Heiner Kuhlmann Richard Dikau 《地球表面变化过程与地形》2017,42(11):1623-1635
Vegetation is an important factor influencing solifluction processes, while at the same time, solifluction processes and landforms influence species composition, fine‐scale distribution and corresponding ecosystem functioning. However, how feedbacks between plants and solifluction processes influence the development of turf‐banked solifluction lobes (TBLs) and their geomorphic and vegetation patterns is still poorly understood. We addressed this knowledge gap in a detailed biogeomorphic investigation in the Turtmann glacier foreland (Switzerland). Methods employed include geomorphic and vegetation mapping, terrain assessment with unmanned aerial vehicle (UAV) and temperature logging. Results were subsequently integrated with knowledge from previous geomorphic and ecologic studies into a conceptual model. Our results show that geomorphic and vegetation patterns at TBLs are closely linked through the lobe elements tread, risers and ridge. A conceptual four‐stage biogeomorphic model of TBL development with ecosystem engineering by the dwarf shrub Dryas octopetala as the dominant process can explain these interlinked patterns. Based on this model, we demonstrate that TBLs are biogeomorphic structures and follow a cyclic development, during which the role of their components for engineer and non‐engineer species changes. Our study presents the first biogeomorphic model of TBL development and highlights the applicability and necessity of biogeomorphic approaches and research in periglacial environments. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
139.
Population of Daphnia carinata exposed to different times on the day showed sharp inhibition of reproduction (measured different life table data) on the day of solar eclipse as compared to pre- and post-eclipse days. Sudden fall of water temperature and abrupt change to darkness as prevailed during the solar eclipse were responsible for inhibition of reproduction in Daphnia carinata. Cold and dark induced reproductive inhibition was also confirmed in a simulated experiment mimicing eclipse reduction in light and temperature. 相似文献
140.
Sarah McMullan Denis Vida Hadrien A. R. Devillepoix Jim Rowe Luke Daly Ashley J. King Martin Cupák Robert M. Howie Eleanor K. Sansom Patrick Shober Martin C. Towner Seamus Anderson Luke McFadden Jana Horák Andrew R. D. Smedley Katherine H. Joy Alan Shuttleworth Francois Colas Brigitte Zanda Áine C. O'Brien Ian McMullan Clive Shaw Adam Suttle Martin D. Suttle John S. Young Peter Campbell-Burns Richard Kacerek Richard Bassom Steve Bosley Richard Fleet Dave Jones Mark McIntyre Nick James Derek Robson Paul Dickinson Philip A. Bland Gareth S. Collins 《Meteoritics & planetary science》2024,59(5):927-947
On February 28, 2021, a fireball dropped ∼0.6 kg of recovered CM2 carbonaceous chondrite meteorites in South-West England near the town of Winchcombe. We reconstruct the fireball's atmospheric trajectory, light curve, fragmentation behavior, and pre-atmospheric orbit from optical records contributed by five networks. The progenitor meteoroid was three orders of magnitude less massive (∼13 kg) than any previously observed carbonaceous fall. The Winchcombe meteorite survived entry because it was exposed to a very low peak atmospheric dynamic pressure (∼0.6 MPa) due to a fortuitous combination of entry parameters, notably low velocity (13.9 km s−1). A near-catastrophic fragmentation at ∼0.07 MPa points to the body's fragility. Low entry speeds which cause low peak dynamic pressures are likely necessary conditions for a small carbonaceous meteoroid to survive atmospheric entry, strongly constraining the radiant direction to the general antapex direction. Orbital integrations show that the meteoroid was injected into the near-Earth region ∼0.08 Myr ago and it never had a perihelion distance smaller than ∼0.7 AU, while other CM2 meteorites with known orbits approached the Sun closer (∼0.5 AU) and were heated to at least 100 K higher temperatures. 相似文献